Mango trees are the specimens of handsome landscapes with round
shaded canopy. The canopy is broad and rounded, or more upright, with a
relatively slender crown. They are very fast growing trees under hot
climate. Its leaves are dark green on the top side and pale at the
bottom, usually red while young. The midrib is pale and obvious with
distinct horizontal veins. The fruit grows at the end of a long, string
like stem (the former panicle), with sometimes two or more fruits to a
stem. The fruit is nutritionally rich in carbohydrates and vitamin A and
C. It is relished and liked due to its flavor, color, dietary and
medicinal importance. The young, immature fruit is an effective antidote
for mild sunstroke, while the mature fruit provides energy to weak and
old ones (Jiskani etai, 2007).

Mango is native of Indian subcontinent but also grown in almost all
continents of the world like North, South and Central America, South,
West and Central Africa, Australia. It is grown in countries like China,
India, Pakistan, Bangladesh, Philippine, Burma, Thailand, Malaya,
Mexico, Brazil, United States of America, etc. In Asia, it is grown on
over 1.0 million ha area and produces over 12.42 million tons per year
(Chadha and Pal, 1993). In Pakistan mango is not only a source of
employment in the countryside, but is also an important foreign currency
earning fruit. It is grown in various southern districts of Sind,
Pakistan such as; Hyderabad, Tando Allahyar, Matiary, Mirpur Khas,
Sanghar and Nawabshah. Several commercial varieties of mango are popular
in these districts which are exported to generate foreign earnings. For
successful growth and development of mango orchard, proper irrigation is
required during critical stages such as flowering, fruiting and
maturity. Irrigation of mango orchards, whether it is young, non-bearing
and/or bearing, is closely related to soil and climate of the orchard.
The fine textured deep and well drained soils with high retention
capacity of water require less irrigation, while very fine textured and
sticky soil, like black cotton requires no irrigation. Other groups of
soils like light and medium textured require adequate surface
irrigation, provided they are well drained. No irrigation is required
for soil having water tables located within three meters from the soil
surface as mango tree roots travel to this depth in search of water.
Climatic factors such as humidity, rainfall and temperature can also
affect the irrigation requirements of the mango orchards. The orchards
situated in humid tropics do not require irrigation irrespective of soil
type while under dry climate having low humidity and high temperature;
irrigation is needed at 15 days interval. Mangoes grown in Brazil
consume about 55.5 cm during a productive cycle (Azevedo et al., 2003).

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Mango trees have very well spread, deep, and extensive root system.
In deep soil the taproot may descend to about 7 meter depth, while
copious of wide-spreading feeder roots also extend many anchor roots
which penetrate by few meters. The main f root develops secondary roots
that go to sub-soil layer. This extensive root system of mango draws and
gets the moisture from far and wider areas. Under extensively spread
root system, only light surface irrigation is sufficient. In some odd
conditions, the extensive root system development is checked by hard pan
rock. In this situation root zone is kept restricted and ultimately it
restricts the vegetative growth of plant. Trees grown in such
environment require rather frequent irrigation for better yield and
quality fruits. A well spread, deep and extensively rooted system of
mango trees requires more moisture as compared to shallow and
horizontally spread roots. The irrigation requirements of young and
non-bearing orchards differ from the bearing orchards. The young and
non-bearing orchards require light and frequent irrigation to boost fast
and vigorous growth of plants. At the initial stage, the root spread of
the plants is limited hence light irrigation at frequent intervals is
required to wet the soil. The non-bearing trees 4-5 years of age are
usually irrigated at weekly interval while the bearing orchards are
irrigated at regular intervals of 10 to 15 days. This interval is a
prime requirement during fruit set and for full fruit development. This
would help attain full sized fruits and avoid fruit drop. For better
flowering and flower bud differentiation the irrigation needs to be
stopped at least for 2-3 months during winter month, because, the
irrigation during this period promotes vegetative growth, which might
have detrimental effects on flowering. Evidences from recent past have
shown that the mango plant suffers from a number of pests and diseases,
which affect different of parts plant at the growth, development,
flowering and fruiting stages. A mango quick decline (MOD) due to mango
sudden death syndrome (MSDS) or mango tree mortality (MTM) is a newly
emerging problem (Jiskani era/., 2007). The scientists have successfully
conducted many experiments to discover the exact causes and suggested
several control measures. They prepared recommendation for growers, to
face the problem and improve the productivity of mango orchards (Khuhro
ef a/., 2006). Some progressive growers have adopted their suggestions
and achieved fruitful results, while most of the growers are still
facing disease problems as they have failed to follow the
recommendations made by the scientists. In some cases the insecticides
and pesticides were ineffective and did not provide any solution; hence
growers are still facing an unknown dilemma and waiting for the
solution. The water shortage at critical flowering and fruiting stages
of mangoes has further added into their desolation.

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Despite having such a well-established irrigation system in the
country, it does not meet total agricultural requirements. The limited
or unavailability of surface water supply at critical stages of mangoes
is another problem faced by the growers. It has been reported by the
Asian Development Bank "Asian Water Development Outlook,
2007", that Pakistan has almost surpassed the water stressed level
and will soon turn into a water scarce country. The country is now
ranked among the worst performers in Asian Nations. This is because of
huge amounts of water lost in the conveyance system, which limits its
availability to the growers especially those at the tail-reaches. Also,
the farming community continues to use water in extravagant and
indiscreet way through traditional flooding methods. They have an
overall efficiency of not more than 30% (Ishfaq, 2002). The water use
efficiency is very poor while the capacity is weakening by every passing
day and quality always keeps worsening. All these indicators suggest
that our agriculture will be suffering through a disastrous phase, if
appropriate measures were not taken on urgent basis to address these
issues.

Water application efficiency needs to be enhanced so that water
could be saved and additional lands could be brought under cultivation,
which otherwise remain barren due to water storage. This could be done
through proper management of current irrigation application methods and
through adaptation of modern irrigation methods. The more emphases
should be focused on the improvement of irrigation efficiency of
application methods. To make efficient use of water for agricultural
production, a precise amount required by the plants be applied at the
right time and at right place with minimal water losses. The modern
micro irrigation methods such as sprinkler, drip, subsurface, pitcher
and bubbler stand a great potential to water saving. These methods not
only have high application efficiency but they produce higher yields.
According to Yildrin and Korukcu (2000) drip irrigation generally
achieves better crop yield and balanced soil moisture in the active root
zone with minimum water losses. On the average, drip irrigation saves
about 70 to 80% water as compared to conventional flooding or furrow irrigation methods (Ishfaq, 2002). Some of the progressive growers have
changed irrigation strategies and now they are applying modern micro
irrigation methods.

The drip irrigation is regarded as one of the highly efficient
methods that allows limited water resource to be properly utilized. The
method not only saves water but also applies fertilizer through
emitters. The drip irrigation allows water near the plant roots either
onto the soil surface or beneath the soil surface directly to the root
zone area. This method has several advantages such as plant attains
quick growth, controls weed, saves labor, applies direct nutrient to
plants, increases yield with quality fruits. The drippers operate at a
very slow rate; usually the discharge matches the soil infiltration rate
which neither allows the surface flooding nor the runoff. Deep
percolation is out of question hence, water losses or minimal. The
fertilizer and nutrient losses are minimal due to localized application
and reduced percolation. It has high water application efficiency, can
irrigate irregular shaped fields without proper land leveling, as is
necessary in case of basin, border and furrow irrigation methods. The
drip irrigation allows safe use of recycled water; maintains moisture
within the root zone near to the field capacity. Even, the soil type
plays less important role in frequency of irrigation in this method. It
also minimizes the soil erosion. The other advantages of drip irrigation
include high uniform distribution of water i.e. controlled by output of
each nozzle. The water system is regulated through valves and drippers
hence labor cost is minimum The Fertigation can easily be included with
minimal waste of expensive fertilizers. The foliage remains dry thus
reduce the risk of diseases. This method usually is operated at lower
pressure than other types of pressurized irrigation systems such as
sprinkler, thus energy costs are reduced (Wikipedia, 2010 and 2011;
Infonet-Biovision, 2010).

Despite having several benefits, drip irrigation method also has
certain disadvantages. The initial cost of the system is very high thus
poor growers cannot afford to install it on their own. The lateral pipes
are made from polyethylene tubes, which are vulnerable to high
temperatures due to continuous and extended sunshine hours. Hence, the
usable life of these pipes is less particularly in the semi-arid and
arid regions. The longevity is variable, it can result in clogging, if
the water is impure and not properly filtered and the equipment is not
regularly checked and properly cleaned. The herbicides and top dressed
fertilizers need sprinkler irrigation for activation; hence, drip
irrigation might be unsatisfactory. The drip tape winding, disposal,
recycling or reuse is needed; otherwise drip tape will require extra
cleanup costs after harvest. In order to install an economical and
efficient system one must consider the important relevant factors viz.
topography, soil type, crops, their water requirement, agro-climatic
conditions, and suitability of drip irrigation system and its
components. The subsurface drip may be unable to wet the soil surface
for germination in lighter soils. Therefore, a careful consideration is
required to install a drip system in these soils. Almost all the drip
systems are designed for high efficiency; hence one can expect neither
deep percolation nor runoff. The salts applied with the irrigation water
may build-up in the root zone, usually at the edges of the wetting front
(Wikipedia, 2010 and 2011).

A number of irrigation methods such as basin, flood, ring, furrow,
sprinkler and drip are used to irrigate mango orchards in Pakistan and
elsewhere. Each system has advantages and disadvantages as one system
may be suitable for a set of conditions but unsuitable for another.
Therefore, proper selection of an irrigation method is vital for the
better management of mango orchards. The drip irrigation system is
usually applied in those areas where the water supplies are limited and
water available needs to be judiciously used. In this study, a drip
irrigation system has been evaluated in terms of water distribution
pattern around the crop canopy, irrigation frequency, number of emitters
and their orientation. The fruit size, fruit quality, and yield under
drip and furrow irrigation were also compared.

MATERIALS AND METHODS Drip irrigation system installation

Study was carried out at the Talpur Farm located on the South of
Kotri city at a distance of about 15 kilometers. The farm is owned by a
progressive farmer and is spread over an area of about 16 hectares. The
farm is irrigated by the Kalri Baghar Canal also known as 'Karachi
Canal1 that off takes from the Kotri Barrage. A drip irrigation system
was installed on a 6.5 ha piece of the mango orchard farm (plate 1). The
system comprises of a water tank, pumping unit, chemical mixing chamber,
flow release pipe, water cleaning system and network of pipes that
supplies water to mango trees. Each mango tree is irrigated through 4
drippers/emitters connected through micro-tubes to the lateral lines
(plate 2). The laterals are connected to sub-mainline which receive
water from the main line in which water is supplied through a pumping
unit from the source. Two lateral lines have been provided to irrigate
each tree. While, two drippers on each lateral line are fixed at a
distance of one meter between them. Depending on the operating pressure,
the drippers can discharge between 50 and 60 liters per hour. A fully
grown mango tree requires about 120 liters day" l, so the
irrigation application time is to be fixed according to discharge
through each emitter.

RESULTS AND DISCUSSION Farmers' perception

A team of experts visited Jaipur Farm, located at the outskirts of
city of Kotri, in the command of Karachi Canal on the complaint of
growers. It was observed that a significant portion of the mango orchard
was. irrigated by a well established drip irrigation system while, the
rest of the orchard was irrigated by flooding method (plate 3). The
grower and the mango contractor were interviewed for the specific
problems related to drip irrigated mangoes. The grower/contractor had
concerns that a significant fruit drop (falling fruits) and defoliation
(falling leaves) problem was observed under drip irrigated mango/trees
as compared to those irrigated by flooded basins. The grower/contractor
also informed that the quality of drip irrigated fruit was inferior
compared to the basin irrigated trees. At maturity, the drip irrigated
mangoes lost their freshness and quality within few hours after harvest.
Under the circumstances they did of exporters, thus their market value
is significantly affected. According to them, a sound of the stone
inside the fruit could easily be heard with a small shake/movement at
maturity. The team investigated the possible causes of fruit drop and
leaf defoliation.

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General observations

On the average, a tree had canopy radius between 2.8 to 3.2 m. Each
mango tree an irrigated by four drippers (work as low pressure jet
sprinklers). They were installed at a distance of about 0.5 to 0.6 m
from the trunk/stem. Significant moisture was observed within a one
meter radius, while beyond this, the moisture reduced towards the outer
sides of the tree canopy. The number of drippers was not enough to
provide adequate water to meet water requirements of tree. It was
further observed that the orientation of the drippers was inappropriate
as a consequence outer edges of the canopy of tree/plant remained under
irrigated. This caused dry stress in the plant roots located in that
vicinity, which could be avoided by increasing the number of drippers
and through their proper placement around the canopy. The lateral pipes
should run along the circumference around the canopy. If required, the
system should be operated for longer periods so that water could reach
the dry areas around the canopy.

The continuous dripping in the surrounding of the main trunk causes
excessive wetting that may result in a problem of root rot/wilt in long
run. This may also result in root death that ultimately will affect
fruit quality and reduce the yield. It may also be recalled that the
drippers are installed near the main trunk at a distance of about 45 to
60 cm from the stem only which cause such wet stresses (plate 3). While
designing a system, a due consideration needs to given to the placement
of the drippers.

Further, a water application and management problem at farm level
was apparent. Due to power crises/failures the system sometimes did not
operate for a specified period, hence the tree's water requirements
were not properly met. The problem could be resolved by introducing new
irrigation schedules and irrigation frequencies could be devised in such
a way that each tree gets the required amounts as per its consumptive use. The trees could neither be under stressed nor over stressed. Also,
the operational hours should be fixed in such a manner that both
excessive flooding and deep percolation are avoided.

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It is the beauty of drip irrigation that it only irrigates the crop
canopy area, the rest of area remains uncultivated and dry. It was
apparent that most of the area between mango rows was very dry hence
weed growth was restricted. Consequently, the dry soil surface increased
the temperatures as compared to basin/flood irrigated wet areas. Also,
the temperatures during this time of the year are pity high; they
expedite evapo-transpiration which cause quick differential in the
moisture gradients between roots and leaves. The water taken by the
roots does not meet the transpiration demands due to sharp moisture
gradient thus plant leaves appear wilted. It was obvious that the plant
leaves were rather yellow (wilted), particularly during afternoon hours,
while they were lush and green in nearby area irrigated by basins. The
leaves of plants seemed dirty under drip irrigated mangoes as compared
to basin flooded ones. In order to reduce the dryness effects, either
the. entire area is flooded during few times of the year or small
channel/furrows between rows are made. The channels may be flooded at
least once a month during fruiting and maturity periods. The drip
irrigated plants may be washed once a year to remove the dirt sitting in
the leaves this would help increase stomatat activity.

Fruit drop, size, quality and yields related to irrigation Under
normal moisture conditions, the fruit set in mango remains unaffected;
however, the prolonged soil moisture deficit has the serious
consequences. The soil moisture deficiency reduces the fruit size and
its quality and increases the drop of immature mango fruit. During fruit
development period, under hot and dry climate, the irrigation prevents
the drop of immature fruits. Early maturity of fruits was observed under
drip irrigated trees that could be attributed to dry stresses under drip
irrigation method. The drop rate was higher under drip irrigated trees
than basin flooded ones (plate 4). The dropped immature mangoes were
collected under drip and basin irrigated trees. The total number and
weights were recorded. The results suggest that the drop rate was higher
by about 25% under drip irrigated trees as compared to basin flooded
ones. The mangoes dropped under drip irrigated trees have less weight as
compared to basin flooded dropouts. The fruit quality and mango yield
under drip irrigated mangoes was slightly affected. While the basin
flooded mangoes has higher weight with a fresh appearance. It was
further observed that the basin irrigation provided sufficient moisture
to the plants during fruit development and maturity period hence the
fruit quality was better than the drip irrigated mango trees. The better
sized mango fruit with a juicier flavor was observed under basin
irrigated tree's than those from tree under deficit soil moisture
under drip irrigation. These findings suggest that a regular and timely
irrigation is necessary for bearing plants than a deficit and untimely
one. Slightly higher yields were observed under basin irrigated mango
trees. The differences in the total yield between two irrigation methods
could be attributed to water stresses experienced by the drip irrigated
trees. A properly managed drip system can provide uniform water
application around the canopy and avoid stresses; ultimately mango
yields will increase with properly irrigated trees. Similar results have
also been reported in a study conducted by Spreer et al. (2007). Their
results showed reduced yields under deficit irrigation as compared to
the fully irrigated mango trees. However, development and post-harvest
quality of fruits grown under deficit irrigation were not adversely
affected. They further reported that fruit size was increased and fruits
had a higher fraction of edible parts under partial root zone deficit.
According to them, in areas where water becomes a limiting factor,
partial root zone deficit may be applied; this would increase the mango
production. In a recent study Spreer et al. (2009) determined yield
response and fruit size distribution for partial root zone drying (PRO),
regulated deficit irrigation (RDI) and irrigated control trees. They
reported that during normal years the yields of the two deficit
irrigation treatments (RDI and PRO) do not differ significantly, while
in a dry year yield under PRO is higher than under RDI and in a year
with early rainfall, RDI yields more than PRO. In all years PRO
irrigated mango trees had a bigger average fruit size and a more
favorable fruit size distribution. They concluded that deficit
irrigation strategies saved considerable amounts of water without
affecting the yield to a large extent, possibly increasing the average
fruit weight, apparently without negative long term effects. Insect
pests and diseases

No serious problem of any insect pest or disease was observed in
the mangoes. Rarely mango midge and scale insect infestation were
noticed. Few leaves were found infected with tips die back and bacterial
leaf spot diseases (plate 5). Such symptoms may be attributed to
inadequate water and nutrition deficiency.

CONCLUSION

Study was carried out at the Talpur Farm located on the South of
Kotri city at a distance of about 15 kilometers. A significant section
of the mango orchard is irrigated by a well established drip irrigation
system while, the rest is irrigated by flooding method. Investigations
were made to evaluate the performance of drip irrigation in terms of
water distribution, frequency, fruit size, fruit quality, and yield.
Following conclusions were drawn from this study:

* About half of canopy radius had sufficient moisture, while the
outer sides remained under watered and stressed. This was because of
improper orientation of the drippers. The dry stresses could be avoided
by increasing the number of drippers and through their proper
placement/orientation around the canopy.

* Due to power crises/failures, a problem related to water
application timing and frequency was apparent. This disturbed the
irrigation schedules hence crop's water requirements were not
properly met. The problem could be resolved by introducing new
irrigation schedule, frequency and operational hours. Operational times
should be worked out in such a way that both excessive flooding and deep
percolation are avoided.

* Most of the area between the rows of mango trees was very dry
hence weed growth was restricted. Consequently the dry soil surface
increased the air temperatures as compared to basin/flood irrigated wet
areas. Also, the temperatures during maturity period become too high;
which caused speedy moisture gradients between roots and leaves. The
water taken by the roots could not meet the transpiration demands due to
sharp moisture gradient thus plant leaves appear wilted under drip
irrigation compared to flood irrigation.

* The fruit drop rate was higher by 25% under drip irrigated trees
than basin flooded ones. Similarly the fruit quality and mango yield
under drip irrigated mangoes was slightly affected. While the basin
flooded mangoes has higher yield with a fresh appearance. The better
size mango fruit with a juicier flavor was observed under basin
irrigated trees than those under deficit soil moisture under drip
irrigation.

* A problem of root rot/wilt could be expected due to continuous
dripping and excessive wetting in the nearby surrounding of the main
trunk. The wet stresses results in root death which ultimately affects
fruit quality and yield.

* Our qualitative observations suggest that a detailed study at the
site could be initiated for quantitative and solid conclusions. The
study should focus on soil characteristics, soil profile texture, water
application timing, application rate, soil infiltration, hydraulic
conductivity, moisture distribution pattern, soil fertility level,
fruiting behavior, and other relevant parameters. The impact of these
factors along with water through drip system could then be related to
the yield and quality of mango and a final conclusion could be drawn.

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